The present invention relates to a thermal treatment furnace in a system for manufacturing semiconductors, in which an object to be treated, such as a silicon wafer substrate, undergoes various processes such as diffusion and hydrogen annealing.
The pre-treatment in the manufacture of semiconductors involves various processes such as diffusion treatment, chemical vapor deposition (CVD) and hydrogen annealing. Such pre-treatment is performed in thermal treatment furnaces. Of these, hot treatment furnaces such as vertical diffusion furnaces and furnace annealors are utilized particularly for heat treating the object at a high temperature therein.
In such hot treatment furnaces, recovery of the treated object from damage and degradation caused by ion implanters, fellow of phosphorus diffusion layer and hydrogen annealing are achieved.
Referring now to FIG. 6, a known semiconductor production arrangement with a hot treatment furnace will be described briefly.
As illustrated, a through aperture 2 extends through a heater base 1. On the underside of the heater base 1, a liner tube support plate 3 of a doughnut shape is disposed concentrically with the aperture 2. An annular seat 19 of a heat insulating material is placed upon the upper surface of the liner tube support plate 3 at the inner edge of the aperture 2. On the heater base 1, a heater chamber 4 is disposed about the aperture 2. Within the heater chamber 4, a cylindrical heater 5 extends upwardly from the heater base 1 concentrically with the aperture 2. Concentrically disposed in order within the heater 5 are a liner tube 6 and a reaction tube 7, the liner tube 6 extending upwardly from the annular seat 19 and the reaction tube 7 extending upwardly from a reaction tube support member (not shown) with its lower end extending beyond the heater 5.
Running along the exterior wall of the reaction tube 7 is a gas injection pipe 8, one end of which is open to the ceiling of the reaction tube 7 and the other end of which is slidingly connected to a gas supply pipe 9 proximate to the lower end of the reaction tube 7. Provided at the lower end of the reaction tube 7 is an exhaust nozzle 10 which is connected slide fit to an exhaust pipe 11.
A boat 17 carrying thereon a wafer 16 is introduced into the reaction tube 7 and is movable upwardly and downwardly via a boat elevator not shown. The boat 17 is vertically positioned, by means of a boat support jig 13, upon a sealing cap 12 covering the lower end opening of the reaction tube 7. The sealing cap 12 is disposed on a boat elevator not shown. Along the peripheral edge of the sealing cap 12, a seal ring 18 is provided to achieve a sealed connection between the sealing cap 12 and the lower end of the reaction tube 7.
The lower end opening (furnace entry port) of the heater 5 and the exposed lower end of the reaction tube 7 are covered by a scavenger 14 which is in communication with an exhaust duct 15.
When the inside of the reaction tube 7 is heated to a predetermined temperature by the heater 5, the boat 17 carrying the wafer 16 thereon is introduced into the reaction tube 7. Then, a reactive gas such as a hydrogen gas is introduced into the reaction tube 7 through the gas supply pipe 9 and the gas injection pipe 8 to thereby do heat treatment of the wafer 16. After the treatment, an exhaust gas is exhausted through the exhaust nozzle 10 and the exhaust pipe 11.
The scavenger 14 serves to cut off radiant heat radiated from the entry port of the heater 5 and to capture particles generated at the furnace entry port, and to capture gas leaked from the connection between the gas injection pipe 8 and the gas supply pipe 9, from the connection between the exhaust nozzle 10 and the exhaust pipe 11 and from the junction between the sealing cap 12 and the reaction tube 7 to cause them to be exhausted through the exhaust duct 15 outside the arrangement.
The scavenger 14 is provided with openings for allowing insertion of the gas supply pipe 9 and the exhaust pipe 11, leaves a gap at the mount portion with respect to the heater base 1 and has a lower end opening for allowing upward and downward movement of the sealing cap 12, producing insufficient sealing effect thereat. As a result, it is not possible to completely capture the gas leaked from the connection between the gas injection pipe 8 and the gas supply pipe 9, the connection between the exhaust nozzle 10 and the exhaust pipe 11, and the junction between the sealing cap 12 and the reaction tube 7, as mentioned above, resulting in leakage of the gas outside the scavenger 14. Further, since sealing between the sealing cap 12 and the lower end of the reaction tube 7 is obtained by use of a single sealing ring 18, it is possible that gas will leak out from such sealed portion.
Thus, it was possible that on certain conditions, explosion of the leaked hydrogen gas will occur during the heat treatment of the wafer in the reaction tube into which hydrogen is introduced. It was also possible that when the reactive gas is of high acidity, the metal portions of the arrangement will corrode. Moreover, the leaked gas will deteriorate the working conditions.